Hell, there are tons of examples of people being arrested for things that aren't crimes at all, and even for acts that are constitutionally protected. Police don't care because they know they'll get away with it (and might even get a paid vacation) when the case against the person who was arrested and likely lost their job as a result gets thrown out. If the unlawfully arrested person is lucky and/or wealthy enough to afford a good lawyer they might get a decent amount of tax payer money out of it.